Our overall objective of this proposal project is to determine the nucleotide sequence of DNA from polyoma virus and simian virus 40 (SV40). The research work will be carried out in 2 stages. (a) To determine the 5 feet yields 3 feet orientation of each DNA strand in a particular DNA fragment with respect to the strands in the neighboring fragments. (b) To determine the nucleotide sequence of several DNA fragments from each type of tumor virus DNA.